Compounds according to the present invention are used to inhibit or treat HDAC-mediated diseases. Examples of such diseases include, but are not limited to, cell proliferative diseases such as cancer, autosomal dominant diseases such as Huntington's disease, genetic metabolic diseases such as fibrosis diseases, for example, cystic fibrosis, hepatic fibrosis, kidney fibrosis, pulmonary fibrosis and skin fibrosis, autoimmune diseases such as rheumatoid arthritis, acute/chronic neurological diseases such as diabetes, stroke, hypertrophy such as cardiac hypertrophy, congestive heart failure, amyotrophic lateral sclerosis, glaucoma, ocular diseases (associated with angiogenesis), or Alzheimer's disease.
Transcriptional regulation in cells is a complex biological process. One basic principle in transcriptional regulation is based on the posttranslational modification of histone proteins, namely histone proteins H2A/B, H3 and H4 forming the octameric histone core complex. The complex N-terminal modifications at lysine residues by acetylation or methylation and at serine residues by phosphorylation constitute part of the so called “histone code” (see Strahl & Ellis, Nature 403, 41-45, 2000).
In a simple model, acetylation of positively charged lysine residues reduces affinity to negatively charged DNA, which now becomes accessible for the entry of transcription factors.
Histone acetylation and deacetylation is catalyzed by histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. HDACs are associated with transcriptional repressor complexes, switching chromatin to a silence structure, transcriptionally inactive. (see Marks et al., Nature cancer Rev. 1, 194-202, 2001). The opposite is activated by HATs which are associated with transcriptional activator complexes. Three different classes of HDACs have been known so far, namely class I (HDAC 1-3, 8; Mr=42-55 kDa) primarily located in the nucleus and sensitive toward inhibition by Trichostatin A (TSA), class II (HDAC 4-7, 9, 10; Mr=120-130 kDa), which exhibits TSA sensitivity, and class III (SIRT2) that are distinct by their NAD+ dependency and TSA insensitivity.
Histone deacetylase (HDAC) inhibitors constitute a new class of anti-cancer drugs having cell differentiation and apoptosis inducing activity. By targeting histone deacetylases (HDACs), HDAC inhibitors affect Chromatin structure by histone acetylation, inducing reprogramming of a complex transcription, for example, reactivation of tumor suppressor genes and repression of oncogenes. Besides acetylate the N-terminal lysine residue in core histone protein, HDAC inhibitors target non-histone protein, important for cancer biology, including heat-shock-protein 90 (HSP90), tubulin or the p53 tumor suppressor protein. Thus, the medical use of HDAC inhibitors might not be restricted to cancer therapy, since efficacy in animal models for inflammatory diseases, rheumatoid arthritis and neurodegeneration has been shown.
HDAC inhibitors known up to now can be classified according to their structure into four categories: 1) short-chain fatty acids (butyric acid and valproic acid); 2) hydroxamic acids (trichostatin A, SAHA, and LBH-589); 3) cyclic peptides (desipeptide); and 4) benzamides (MS-275, and MGCD-0103) (Emanuele et. al., International Journal of Oncology 33, 637-646, 2008). These many histone deacetylase (HDAC) inhibitors (SAHA, LBH-589 and MS-275 etc.) inhibit cell growth, and effectively induce cell differentiation and apoptosis of various transformed cells not only in culture media but also in animal models (Paul A. Marks et. al., Curr Opin. Oncol. 13, 477-483, 2001). Therefore, HDAC inhibitors such as SAHA, LBH-589 and MS-275 have been assessed in clinical studies for the purpose of treating various cancers (Johnstone. R. W, Nat. Rev. Drug. Discov. 1, 287-299, 2002). Representative compounds, currently known as HDAC inhibitors, include SAHA (U.S. Reissue Pat. No. 38506, Zolinza, Vorinostat), PXD101 (WO 02/30879, Belinostat) and LBH-589 (WO 02/22577, Panobinostat), which are hydroxamate compounds, and MS-275 (EP Patent No. 0847992 Entinostat) and MGCD0103 (WO 04/69823, Mocetinostat), which are benzamide compounds. Among these compounds, SAHA was approved on October 2006 and has been used as an agent for treating CTCL (cutaneous T-cell lymphoma), and indications thereof have been expanded additionally, but it is known that SAHA is insufficient in terms of efficacy and side effects (Maiso et al., Cancer Res 66, 5781-5789, 2006).
Although many HDAC inhibitors have been reported to date, there has been a need for effective HDAC inhibitors that are more efficacious and have less side effects (Dokmanovic, et al. Mol Cancer Res, 5, 981-989, 2007).